Orexin 2 receptor–selective agonist danavorexton improves narcolepsy phenotype in a mouse model and in human patients

Significance Despite the discovery of the orexin (hypocretin) neuropeptides in 1998 and their role in narcolepsy type 1 (NT1), current pharmacotherapy addresses only the associated symptoms and not the underlying loss of orexin. Danavorexton (TAK-925) is an orexin 2 receptor (OX2R)–selective agonist that was developed to address the loss of orexin signaling in NT1. Here, we present promising results from preclinical mouse studies through to human clinical studies, which support the therapeutic potential of OX2R-selective agonists for the treatment of NT1. Improvements in excessive daytime sleepiness were also observed in individuals with narcolepsy type 2, indicating that OX2R-selective agonists could also provide therapy for sleep disorders that involve partial or no impairment of the orexin system.


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The secondary objectives were: to investigate the PK of multiple doses of danavorexton in healthy adults and in individuals with NT1 and NT2 (the MRD study only); and to investigate the PD of danavorexton after single IV administration in individuals with NT1 (SRD study) and multiple IV administration in individuals with NT1 and NT2 (MRD study), primarily by evaluating sleep latency on MWT, daytime sleepiness (as measured by the Japanese version of the ESS [JESS]) (6), and number of cataplexy episodes (NT1 only). Exploratory objectives included evaluating the PD effects of danavorexton when administered as a single dose using the KSS (SRD study), and after multiple doses using the PVT and PGI-C (MRD study).

Study design and schedule of procedures
Both studies were conducted at three sites in Japan. Danavorexton was administered as a continuous IV infusion over 9 hours in saline. Rationale for dose selection for the first-in-human SRD study followed US Food and Drug Administration guidance on human equivalent dose calculation, based on allometric scaling and no observed adverse effect levels determination in the most sensitive species (7). In addition, pharmacology studies conducted in mice were taken into consideration. Observed differences in sensitivity between WT and orexin/ataxin-3 mice led to the targeted plasma concentrations in the first NT1 cohorts. The first dose-level cohort (danavorexton 7 mg) was designed to obtain safety and tolerability information following a single dose of danavorexton administered via IV infusion, as well as to obtain the information on PK parameters that would determine the infusion rate and dose levels in subsequent cohorts.
Subsequent doses were determined depending on the available safety, tolerability, and PK data of previous doses. In the MRD study, dose escalation in all parts was determined based on the available safety, tolerability, PK, and PD data from previous cohorts and from the SRD study. In individuals with NT1, a starting dose of 11 mg was considered to be appropriate to examine safety, PK, and PD when dosed daily for 7 days. An effective dose level for individuals with NT2 was considered to be similar to that for healthy volunteers, rather than the dose for those with NT1.
The SRD study part 1 was a randomized, placebo-controlled study, which first evaluated cohorts receiving a single IV dose of danavorexton 7-134.4 mg compared with placebo. Block randomization was used to ensure that six participants received danavorexton and two participants received placebo in each dosing period. Two additional, subsequent parallel cohorts of eight participants were randomized 6:2 to danavorexton and placebo, and they received higher doses of 180 mg and 240 mg each. One parallel cohort of healthy elderly participants (n = 8, randomized 6:2 to danavorexton 112 mg and placebo) was evaluated. One open-label cohort of healthy participants receiving danavorexton 112 mg (n = 4) had CSF collection for PK analysis.
The SRD study part 2 consisted of three NT1 cohorts, each conducted as a randomized, doubleblind (except for a sponsor unblinded team), placebo-controlled, two-period, crossover study to assess the effect of danavorexton on maintaining wakefulness. The three cohorts were dosed as follows: danavorexton 5 mg and placebo (n = 6); danavorexton 11.2 mg and placebo (n = 4); and danavorexton 44.8 mg and placebo (n = 4).
All three parts of the MRD study were randomized, double-blind, placebo-controlled studies to assess the safety, tolerability, and PK of danavorexton administered via IV infusion in healthy adults (part A), individuals with NT1 (part B), and individuals with NT2 (part C). Part B and part C also included assessments of PD effects in NT1 and NT2. In all parts of the MRD study, danavorexton or placebo was administered via IV infusion over 9 hours once daily for 7 days.
The MRD study part A was planned as two cohorts (A1 and A2; danavorexton 44 mg and 112 mg, respectively) plus one additional cohort (A3; danavorexton 180 mg). Each cohort consisted of eight healthy adults randomized to danavorexton or placebo in a 6:2 ratio in a double-blinded fashion.
The MRD study part B was planned as two cohorts (B1 and B2; danavorexton 11 mg and 44 mg, respectively). Each cohort consisted of six individuals with NT1 who were randomized to danavorexton or placebo in a 4:2 ratio in a double-blinded fashion. In part B, an exploratory PD assessment was conducted to evaluate the potential efficacy of danavorexton using MWT, KSS, cataplexy frequency assessment, PVT, and PGI-C.
The MRD study part C was planned as two cohorts (C1 and C2; danavorexton 44 mg and 112 mg, respectively). Each cohort consisted of six individuals with NT2 who were randomized to danavorexton or placebo in a 4:2 ratio in a double-blinded fashion.
Participants underwent NPSG on day −2 and baseline MWT sessions four times on day −1 (at approximately 10:00, 12:00, 14:00, and 16:00). Study drug dosing via IV infusion was started at approximately 08:00. MWT was conducted on day 1 at approximately 10:00, 12:00, 14:00, and 16:00. Participants were allowed to take a nap on the days with no MWT assessment. On day 7, the participants underwent MWT at the same hours as on day −1. Cataplexy was recorded using a sleep diary.

Study populations
The SRD and MRD studies both enrolled healthy adults and individuals with NT1. The SRD study also enrolled healthy elderly participants, while the MRD study enrolled individuals with NT2. In the SRD study part 1 and the MRD study part A, eligible healthy adults were 20-55 years of age (inclusive), had a BMI of ≥18.5 kg/m 2 but ≤30.0 kg/m 2 , had a body weight of ≥50 kg, and were normotensive at screening (SBP <140 mmHg and DBP <90 mmHg) with no history of hypertension or use of antihypertensive medication. In the SRD study part 1, eligible healthy elderly participants were 65-80 years of age (inclusive), had a BMI of ≥18.5 kg/m 2 but ≤30.0 kg/m 2 , had a body weight of ≥40 kg and were normotensive at screening (SBP <140 mmHg and DBP <90 mmHg) with no history of hypertension or use of antihypertensive medication.
Participants with any significant comorbid medical disorders were excluded. All stimulants and anti-cataplectic medications were stopped prior to the baseline visit for ≥1 week (tables S8 and S9; none of the participants had used sodium oxybate).
In the SRD study part 2 and the MRD study part B, eligible participants had a diagnosis of NT1 as defined by the International Classification of Sleep Disorders-Third Edition, an ESS score of ≥10, an average (of four sessions) baseline MWT sleep latency of ≤20 minutes, and no sleep latency of ≥30 minutes in any single session, and they had tested positive for HLA-DQB1*06:02. They were 18-80 years of age (inclusive), had a body weight of ≥40 kg, and had an SBP <140 mmHg and DBP <90 mmHg. In the MRD study, participants with NT1 had to have experienced at least three episodes of cataplexy per week during the screening period.
In the MRD study, inclusion criteria for participants with NT2 were the same as for participants with NT1, except that participants had a diagnosis of NT2 as defined by the ICSD-3 and there was no cataplexy criterion.

PK evaluation
Plasma (SRD and MRD) and CSF (SRD only) concentrations of danavorexton were measured using validated HPLC-MS/MS methods. In the SRD study part 1, blood samples for PK analyses were collected from healthy participants before infusion, at 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 9 hours after the start of infusion, and at 0.17, 0.33, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 10, and 15 hours after the end of infusion. In the SRD study part 2, blood samples from individuals with NT1 were collected before infusion, at 1, 2, 4, 6, and 9 hours after the start of infusion, at 0.17, 0.5, 1, 2, and 15 hours after the end of infusion, at bedtime, and upon awakening. In the SRD study part 1, CSF samples (2.5 mL each) were taken 6 hours after the start of infusion for the CSF cohort only (healthy participants, n = 4, SRD study part 1).
In the MRD study part A, blood samples for PK analysis were taken before the start of infusion, 0.5, 1, 1.5, 2, 4, 6, 8, and 9 hours after start of infusion, and 0.17, 0.33, 0.5, 0.75, 1, 1.5, 2, 3, 6, 10, and 15 hours after end of infusion on days 1 and 7. In the MRD study parts B and C, blood samples were taken before the start of infusion, 1, 2, 4, 6, and 9 hours after start of infusion, and 0.17, 0.5, 2, 6, 10, and 15 hours after end of infusion on days 1 and 7. For all parts of the MRD study, blood samples were also taken before the start of infusion and 9 hours after the start of infusion on days 5 and 6.
The lower limit of quantitation of danavorexton was 0.2 ng/mL for plasma and 0.1 ng/mL for CSF.

PD assessments (SRD study part 2 and MRD study parts B and C)
The MWT is a validated objective measure of the time taken for a person to fall asleep under soporific conditions (semi-reclined position and trying to stay awake, lights on) as determined using EEG. The MWT has been routinely used in clinical trials of drugs approved to treat EDS in narcolepsy (8,9). Four 40-minute sessions of the MWT were performed at approximately 10:00, 12:00, 14:00, and 16:00, and participants were required to stay awake during intervals between sessions. In the SRD study, the MWT was performed on day 1 only. In the MRD study, the MWT was performed on day −1, day 1, and day 7.
The KSS is a Likert-type, nine-level, self-report scale that measures the subjective level of sleepiness at a specific time point during the day. Participants indicate which level best reflects their sleepiness experienced in the past 10 minutes (10). The KSS was rated at baseline and hourly until 11 hours after infusion start. In the SRD study, the KSS was performed on day −1 and day 1. In the MRD study, the KSS was performed on day −1, day 1, and day 7.
The ESS measure of EDS is a subjective, self-recorded rating scale of the tendency to fall asleep in eight defined situations of daily life. A four-point scale (scored at 0-3) is used to answer each of the eight questions to give a total in the range 0-24. Higher scores indicate stronger subjective daytime sleepiness, and scores <10 are considered to be normal. In studies TAK-925-1001 and TAK-925-1003, the JESS was used to evaluate subjective sleepiness, and participants were asked to consider the past 7 days when completing the survey (6). In the SRD study, the ESS was only used as a baseline measure. In the MRD study, the ESS was assessed on day −1 and The PVT is a simple reaction performance task that measures behavioral alertness and sustained attention by recording reaction times to visual stimuli. In study TAK-925-1003, a 10-minute version of PVT was used; an inter-stimulus interval was set at between 2 seconds and 10 seconds. In the MRD study only, the PVT was assessed on day 1, day −1, and day 7.
The PGI-C is a seven-point self-report measure of the perceived efficacy of treatment. Patients rate their perceived change from 'very much improved' to 'very much worse.' In the MRD study only, the PGI-C was assessed on day 7.
Assessment of cataplexy episodes (the MRD study part B only) was conducted in individuals with NT1 based on sleep diary and self-reported questionnaires, and time of event(s) was captured.

Safety assessments
For both studies, a TEAE was defined as an adverse event (AE) that occurred on or after the start of study drug administration. A related TEAE was defined as an AE that followed a reasonable temporal sequence from administration of a study drug, or for which a causal relationship was at least a reasonable possibility. Safety measures included: reported AEs; vital signs, including pulse rate, and BP (BP was checked with the participant lying in a bed with the head of the bed inclined at 30 degrees); body weight; 12-lead and Holter ECG; and clinical laboratory tests (hematology, chemistry, urinalysis).

Statistical analysis
For each study, three analysis sets were used: the safety set (all participants who received at least one dose of study drug); the PK set (all participants who received at least one dose of study drug and provided sufficient PK measurements to estimate at least one PK parameter); and the PD set (all participants who received at least one dose of study drug). Plasma and CSF concentrations of danavorexton were summarized for each scheduled sampling time using descriptive statistics. Plasma and CSF PK parameters of danavorexton were summarized using descriptive statistics. In both studies, PD outcomes were described using descriptive statistics and, when appropriate in the MRD study, the effect of danavorexton was evaluated with a linear mixed effects model. The model included treatment (each dose level of danavorexton and placebo), day (as a categorical variable), the treatment-by-day as fixed effects, baseline average sleep latency in the MWT as a covariate, and participant as a random effect. TEAEs were coded using the Medical Dictionary for Regulatory Activities.